Metallic shell



Get. '19 1926.

B. BART METALLIC SHELL Original Filed Jan. 1. 1923 patented Got 19,1926,

u stares METALLIC SHELL.

Original application filed January 11, l923ySerial'No. 612,133.

November 10, 1923.

The'invention relates toa thin metallic shell formed by the deposit'of-metalon a glass mold and usedlas'a grinding tool, in which aspect ofthe disclosure this application is a division of application, Serial No.612,133, both filed January 11, 1923.

One-of the objects of the invention is to provide a thin metalshellwhich will be an exact replica of a'pr-epared' surface of a glassmold and the surface-of which so' formed on themold shall beof fine,homogenous particles cohering toproduce a smooth continuous surfacecorresponding in the minutest details to the surface of the mold.

I attain this phase of the invention by depositing the metal" as fineparticles on the mold surface either'by depositing astream of metal onthe mold to form a thin layer asmore particularly described in'my pendingapplication, =-Serial No. 387,974, filed June 10, 1920, or by formingon the mold a thin metal coating by electrolytic precipitation.VVhe're-thesh'ell is tobe utilized as the replaceable toolof a agrinding chuck it is preferably formed of ,electrolytically depositedcopper as'descr-ibed inapplicatlon, Serial No. 612,138, due "toits'capacity to reproduce faithfully the moldsurfacein'all its detailsand due tojthefiffectiveness ofthe smooth surface -when formed-ofelectrochemically fdepositedcopper as a grinding The inventionrelates specifically toan im provement in the art of forming metallicreflectors of the type "generally known as parabolic or sphericalreflectors." It is a commercial requirementof such reflectors that thecurved-portions'be outlined'by a flat outstanding attaching orreinforcing 1 flange. As such reflectors must be formed on similarshaped-glass molds and as these molds must be molded andpolished tothedesired shape, the invention features a shell having the sameconfiguration, including the flange, as the finished reflector and whichcan .be utilized to form or grind the. molds to shape.

Another-object ofthe invention is to provide a simple form ofshell,-which can be produced in large numbers from a single masterm0ld,all of'which willhave surfaces exactduplicates of-each-other andofthe and which; can be constructed without deleterious action or wear onthe master mold. Further featuring economy 1n construction Divided andthis application f led Serial No. 673,976. a

meansof the reflector, be formed accurately with relation to theopticaXis or other point of referenceof the-reflector.

Accordingly,.another object of the present disclosure is to, provide aform of mold so that it willact to form exactly the desiredconfiguration and dimensions of the curved or parabolic portion of thereflector, as well as its associated outstanding flange and which willinsure the definitelocatingof the flange with referenceto the curvedportion of-it'he reflecting surface. .Various other objects andadvantages of the invention .will be'in; part obvious from 'aninspection of the accompanying-drawings and inwpart will-be more fullyset forth'in the "following '--particular "description of one form of'inecha'nism embodying my invention, .'-and' the. invention alsoconsists in icertainunew and novel features of'con--'st-ruction1:andcombination of parts hereinafter set'forth and claimed.

a In the drawings: Figure.- tratinga means for forming the shell bychemical-reaction on a rotating glass mold; Figure 2 is aplan view of.the mold shown in Figure 1;

Figure 13 is a view largely in diagrammatic outline'ofan electrolytic{tank illustrating a means for forming the shell byelectrolyticprecipitation on a mastermol'd; Figure 4 is an; axialsectional view of a grinding chuck illustrating a use of the shell -Whenemployed as the grindingtool ofsuch a chuck; and I I Figure 51sft'nPGlSPQC'ElVQ view of the shell "formed by any o f'the methodsherein-disclosed, and which may be used'to illustrate a ---.grindingtool. .1

correspondingsurface of "themaster mold,

fj'There is shown in Figure'l a master mold 10, thefcentral portion"ofwhich. isconvezed with 1 a forming surface 11, symmetrically 1'isiaiview'in axial section illusiii tion indicated by the line a-O. 1nthe device illustrated the mold is intended to define the reflectingsurface of a parabolic reflector indicated at 12 and provided with anoutstanding flange 13. However, it is obvious that the shell 12 may beused for other purposes and as an illustration of such other use it maybe employed as the replaceable tool of a grinding chuck for the purposeof grinding molds such as is shown at 10.

The flange 13 of the shell, reflector or tool, is formed on the upperside of an outstanding flange 14:, which projects integrally from thecurved portion of the glass mold. The top surface 15 of the flange 1 1is contained in a plane normal to the line (1-4), that is, at rightangles to the optic axis of the reflector. The flange 14 is outlined byan upstanding rim 16, which rirn provided with a plurality of over-flowrecesses 17.

The glass mold is mounted for rotary movement about the axis 66"?) andfor this purpose is operatively connected to a power shaft 18. A sprayof metal capable of forming. a reflecting or grinding surface isdirected on to the surface of the mold from a depositing apparatusindicated symbolically by the spray nozzle 19, and the nozzle 19 mayrepresent a drip nozzle of the type disclosed in my application, SerialNo. 67 3,97 5. In operation and assuming for instance that it is desiredto provide a sliver faced parabolic reflector, a fine spray of asolution of silver, together with a reducing reagent of the type usuallyemployed in such operations, is directed through the nozzle on to theglass mold adjacent its crown portion 20, and while the mold is rotatingat low speed a silver film will form on the. glass mold and flow downthe inclined sides of the glass mold and on to the outstanding flange."The operation is continued until the desired thickness of metal, whichis usually about one-one hundred thousandth of an inch, accumulates ontop of the curved and flange portion of the glass mold. Any surplus ofmetallic fluid accumulating on the flange will overflow through therecesses in the rim and in this way the thickness of the flange portionof the reflector is regulated.

The thickness of the deposit on the curved portion of the mold isregulated in two ways; first, by varying the VQ OCHY of feed of thesilver solution and its reducing reagent; and second, by regulating thespeed of rotation of the mold itself. It is obvious that at the higherrates of rotary speed there will be developed greater centrifugal forceswhich will tend to whirl the more or less mobile coating toward theperiphery of the mold before the silver has solidified, conversely atrelatively slow speed the layer will tend to accumulate adjacent itspoint of application. Further, by ncreasing the proportion of reducingagent to s lver soluof an inch.

tion, the more rapid will be the formation of the metallic silver andconsequently the greater will be the depth of the formation adjacent thepoint of applicat cn on the mold.

\Vhen the desired coating of silver is formed on the mold, it is theusual pract ce to separate the mold, with the coating so formed, fromthe driving parts indicated by the shaft 18 and to mount the coveredmold in an electrolytic tank where the coating is backed by a layer ofmetal, usually copper or nickel.

The overflow recesses formed in the rib provide convenient means forsecuring the electrodes. Preferably the mold is not highly polished inthe recesses 17 but is matted so as to provide a relatively r nighsurface. The effect is that the reduced silver solution tends toaccumulate at the reces es and in this way there is formed an electricconnection between the shell and the electrodes which connection is ofrelatively great crosssection and therefore of imp oved conductivity. Inthis way a positive electric connection is provided between the severalelectrodes and the extensive area of the silver faced flange. Theportion of the glass rim between the recesses provides insulators between the electrodes.

When the proper thickness of electrolytically deposited backing hasformed, the metallic shell is readily removed from the glass mold bysubjecting the same to a heat treatment. This is most convenientlyattained by spraying hot water on the back of the shell which issufficient to expand the shell and thus readily separate the shell fromthe glass mold. Usually, it will be l'lcCGSSELIY to trim the resultingshell at the po'nts which fitted in the recesses, but this will beimmaterial as it is not extensive.

In case it is desired to formthe shell by electrolytic precipitation themold 10 is p0- sitioned in an electrolytic tank 18, such for instance,as a tank containing copper electrolyte 19 with copper anode plates 20and there subjected to the usual copper precipitation by electriccurrent admitted to the tank through leads 21. A thin bowl shaped layer22 of copper is formed on the curved and adjacent flat faces of the moldand the electrolytic precipitation is continued until a layer of thedesired thickness is provided. On the ground of economy, however, thiscopper layer will be extremely thin, usually an amount merely suflicientto cover the mold completely, about twenty-five thousandths Under somecircumstances the copper layer is strengthened in any manner in whichthin metallic shells are strengthened, and it is herein suggested thatan outer layer of nickel 23 may be precipitated electrolytically on theback of the copper layer. This is done usually by transferring the liliimold with its copper coating to a nickel depositing tank where a desiredthickness of nickel is formed on the back of the copper.

The inner copper layer, hereinafter referred to as a grinding tool withor without the nickel backing, is removed from the master moldpreferably by pouring warm water over the layer. The heat from the hotwater causes the thin metal to expand and due to difference inco-efiicient of expansion between metal and glass the metal shellseparates readily from the glass especially when the insertion of aknife between the metal layer and the glass permits the entrance of airbetween the glass and the coating.

The tool thus formed is placed in a grinding chuck of conventionaldesign and one form of which is shown in outline in Figure 4:. Thischuck includes a driving shaft 24 on which is fitted aniron bowl 25which corresponds somewhat to the old grinding chuck and is of courseformed approximately to shape so as to receive with a. fairly snug fitthe tool for which it is intended. A tool formed as described isfastened to the iron bowl usually by means of screws 26 passed throughapertures 27 in the flange 13 of the tool and into the periphery of thebowl 25. The chuck is thus equipped for operation and is designed torotate usually at low speed about an axis of rotation indicated by theline 0cZ and which is co-incident with the line ab in so far as the toolis concerned.

While specific reference is made in this feature of the disclosure tocopper as the precipitated metal it will be understood that this metalis suggested due to its relative cheapness and due to the effectivenessof forming a uniform layer of such metal, but copper is to be regardedsimply as an example of one suitable metal used in forming such shells.In other cases as where a brilliant reflector is desired the use of someother metal, such for instances, as silver is sug gested. lVhenconstructed for use as a grinding tool the shell is positioned in agrinding chuck of conventional design as more fully disclosed inapplication, Serial No. 612,133.

Having thus described my invention, I claim:

A thin metallic shell constituting a tool for grinding flanged parabolicglass molds, said tool adapted to be rotated about an axis and beingsymmetrical relative to said axis, said tool comprising a curved centralbody portion parabolic in cross section through its axis and outlined atits periphery with an integral outstanding flange, said flange being ina plane perpendicular to the axis of the parabolic central portion, oneside of the tool constituting a grinding surface accurate to molecularproportions.

Signed at New York city, in the county of New York and State of NewYork, this 31 day of October A. D. 1923.

BLASIUS BART.

